PITCH fibre

Summary of Known Methods of Ereparation of Mesophase. At the time of writing, it appears that a major objective of research into the chemistry of mesophase formation is to obtain mesophase at as low a temperature as possible and to have a soluble mesophase, e.g. in 1,2,4 trichlorobenzene (112). The applications of such mesophase(s) must be in the production of graphitizable pitch fibres. However, this direction of research could have applications in many other areas of carbon/graphite production. Therefore it is appropriate, now, to make a list of known methods of preparation of mesophase (113). 

Precursor (for Carbon Fibre)—Either the PAN or pitch fibres from which carbon fibres are derived. 

Research in ACF has attracted increasing attention in the last few years in terms of their synthesis, and their suitability in different applications that include solvent recovery, molecular sieving, gas storage and catalysis. Activated carbon fibres are usually prepared from precursors of low or intermediate crystallinity such raw materials include polyacrylonitrile (PAN) fibres, cellulose fibres, phenolic resin fibres, pitch fibres, cloth or felts made from them, and viscose rayon cloth. They are first pyrolysed and then activated at a temperature of 700-1000 C in an atmosphere of steam or carbon dioxide. Both the processing costs and the properties of the fibre products are dependent on the nature of the starting material. 

Macia-Agullo JA, Moore BC, Cazorla-Amoros D, Linares-Solano A. Activation of coal tar pitch fibres physical activation vs chemical activation. Carbon 2004 42(7) 1367-1370. 

The first pitch carbon-fibres were prepared by Otani" by the pyrolysis of PVC-pitch fibres which were obtained by extruding molten pitch through a pinhole in the bottom of the cell used for melting... 

The hot stretching process for the production of pitch carbon-fibres is a difficult and costly process. Thus attempts have been made to produce oriented carbon-fibres from other varieties of pitch materials. One such approach employed special pitches consisting of aromatic molecules with structures capable of forming anisotropic pitch fibres. 

The spinning temperature and the type of spinning process also determine the structure of the final carbon fibre. For example, the radial structure of mesophase-pitch fibres is caused by a laminar flow of mesophase pitch through a spinneret and can be suppressed by changing the laminar flow to turbulent flow. Carbon fibres with different structures have been produced using spinnerets of different shapes (Figure 6). 

Simi lar effects have been found in the modulus of elasticity results, with different investigators all finding linear relationships between elastic modulus and fibre content, but with quite different slopes. In particular, the addition of pitch fibres does not lead to any significant increase in modulus of elasticity, reflecting the fact that their modulus of elasticity is similar to that of the matrix. The addition of PAN fibres does increase the elastic modulus, as their modulus of elasticity is much greater than that of the matrix. 

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